This invention relates generally to devices for carrying cutting and drilling tools and more particularly to devices for raising and lowering cutting heads of decoking units for residual oil delayed coking reactors.
In the last phase of petroleum refining, the heavy petroleum remaining is fed into very large coking drums and heated to a temperature sufficient to extract all remaining volatile materials leaving a residue in the drums of solid coke which is substantially free of volatiles. Decoking must be performed on the drums in order to prepare them for further use. Commonly high pressure water jet cutting nozzles are employed to drill and cut the coke sufficiently to allow it to be flushed from the coking drum. The water is supplied to the nozzles at a rate of about 2000 gallons per minute and a pressure of about 3000 pounds per square inch. The cutting nozzle for each coking drum has its own valve fed from a manifold which is fed by an upstream decoking control valve. In addition, a bypass valve is employed, to shunt water back to the jet pump suction tank, for those times when all drums are closed off from the manifold.
Since the coking drums are commonly of the order of 60 to 100 feet high, it is necessary that the water jet cutting head be installed on a drill stem sufficiently long to reach the full vertical extent of the drums. Such long drill stems require an equally long vertical travel for the cutting tool. Thus, it has been common practice to build a decoking tower over each coking drum, to mount the cutting tool on a cutting tool carrier, and to raise and lower the tool carrier and the cutting tool using winches and cables. Towers for supporting such equipment may be as high as 200 feet high, or more, and are very large and heavy. They are not movable. Therefore, each coking drum must have its own tower.
In addition, arresting gear is required to prevent a free fall and to save the tool and other equipment in the event of a cable break or a winch failure. This redundancy adds significantly to the cost of the decoking system without contributing to the efficiency of the actual decoking process.
The foregoing illustrates limitations known to exist in present cutting tool carriers. Thus, it would clearly be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.